Fuel cells are electrochemical energy conversion devices that produce electricity catalytically from external supplies of a fuel such as hydrogen and an oxidant such as oxygen in the presence of an electrolyte. Because fuel cells do not combine fuel and oxidant directly through combustion, they produce energy at higher efficiencies and with less hazardous effluent as compared to internal combustion generators. Generally, fuel cells can operate continuously as long as the flow of fuel and oxidant is maintained. This feature, combined with their lack of moving parts, underscores their utility as reliable power sources in remote locations such as spacecraft, isolated weather stations, inaccessible rural locations, and the like.
A proton exchange membrane (PEM) fuel cell, sometimes called a polymer electrolyte membrane fuel cell, normally contains a membrane electrode assembly (MEA), formed by an electrolyte membrane disposed between a pair of catalyst layers, which are correspondingly disposed between a pair of gas diffusion layers (GDL). In a typical PEM fuel cell, hydrogen is oxidized at the anode side of the MEA to form protons and electrons, while oxygen is reduced at the cathode side of the MEA by its reaction with protons and electrons to form water and heat. The electrolyte membrane transports the protons from anode to cathode while the current of electrons flows through an external circuit from anode to cathode to provide power.
Commercial and large scale fuel cell applications still face certain impediments, many of which center around the performance of the catalysts and catalyst layers. For example, to attain desirable operating voltages, large amounts of precious metals such as platinum often are required for the catalyst layers, a feature that increases material costs. Further, at high voltages many useful metal catalysts can react with water, oxygen, and/or other contaminants to degrade catalytic activity and limit the useful life of the fuel cell. As such, there is a continuing need for alternative catalyst materials that can improve fuel cell performance, lower material costs, or enhance catalyst durability.